The present invention relates to an improvement, made to high-precision positive-displacement pipettes intended for the sampling and dispensing of small quantities of liquid.
In the prior art, such high-precision positive-displacement pipettes are already known and are of the type comprising a substantially tubular pipette body, at the lower end of which there is arranged a calibrated capillary tube in which a tight-fitting piston moves against an upward elastic restoring force exerted by a main spring, said piston being controlled in its downward displacement by a control rod projecting from the upper end of said pipette body, as well as an element gripping the upper end of the piston, said gripping element being of the type with resilient arms which move apart radially by displacement against the force exerted by a second spring of a resistance much higher than that of the main spring and said gripping element being solid with said control rod in translation. Such a positive-displacement pipette is described, for example, in Applicant's French Pat. No. 2446672.
The present improvement made to such a type of positive-displacement pepette lies mainly in a special arrangement thereof intended to permit a simultaneous ejection of the capillary nozzle and of the piston, without the operator having to manipulate the capillary and/or the piston directly. It is clear that, in the handling of radioactive samples or any other samples of contaminated liquid, it is crucial to be able easily to ensure such a simultaneous ejection of the capillary nozzle and of the piston which constitute the only elements of the pipette which are contaminated by the sampled liquid.